Sodium butyrate stimulates NHE8 expression via its role on activating NHE8 basal promoter activity

Abstract

FK. Sodium butyrate stimulates NHE8 expression via its role on activating NHE8 basal promoter activity. Am J Physiol Gastrointest Liver Physiol 309: G500 -G505, 2015. First published July 8, 2015; doi:10.1152/ajpgi.00194.2015.-Butyrate is a major metabolite in colonic lumen. It is produced from bacterial fermentation of dietary fiber. Butyrate has been shown to stimulate electroneutral sodium absorption through its regulation on sodium/hydrogen exchanger 3 (NHE3). Although NHE8, the newest addition of intestinal NHE family, is involved in sodium absorption in the intestinal tract, whether butyrate modulates NHE8 expression in the intestinal epithelial cells is not known. In the current study, we showed that butyrate treatment strongly induced NHE8 protein and NHE8 mRNA expression in human intestinal epithelial cells. Transfection with the human NHE8 promoter reporter constructs showed that butyrate treatment stimulated reporter gene expression at an amount comparable with its stimulation of NHE8 mRNA expression. Interestingly, a similar result was also observed in human NHE8 promoter transfected cells after trichostatin (TSA) treatment. Gel mobility shift assay identified an enhanced Sp3 protein binding on the human NHE8 basal promoter region upon butyrate stimulation. Furthermore, Sp3 acetylation modification is involved in butyrate-mediated NHE8 activation in Caco-2 cells. Our findings suggest that the mechanism of butyrate action on NHE8 expression involves enhanced Sp3 interaction at the basal promoter region of the human NHE8 gene promoter to activate NHE8 gene transcription. Thus butyrate is involved in intestinal regulation of NHE8 resulting enhanced sodium absorption.butyrate; NHE8; intestine; Sp3; acetylation BUTYRATE, A MEMBER OF THE short-chain fatty acid family, is produced in large amounts in the colonic lumen by bacterial fermentation of carbohydrates (7). It is important for mucosal homeostasis by modulating cell differentiation and apoptosis (12, 13). Butyrate is the preferred fuel for the colonic epithelial cells and also has significant effects on maintaining colonic health (22). Studies showed that lack of short-chain fatty acids could result in colonic inflammation, such as seen in diversion colitis (11). Decreased availability of luminal butyrate and/or impaired butyrate metabolism have also been found to contribute to ulcerative colitis and pseudomembranous colitis (10, 25).In the intestine, butyrate stimulates sodium absorption by increasing the activity of the epithelial sodium channel (ENaC) and sodium/hydrogen exchanger 3 (NHE3). Unlike sodium channels, which transport sodium following concentration gradient, NHEs mediate the movement of extracellular Na ϩ into cells in exchange for intracellular H ϩ . Multiple NHE isoforms are identified in the intestinal epithelial cells. NHE1 is located at the basolateral membrane in the intestinal epithelial cell and is involved in intracellular pH regulation and cell volume regulation. NHE2, NHE3, and NHE8 are expressed at the apical membrane in th...

SLC9 Gene Family: Function, Expression, and Regulation

“…In the rat distal colon in vitro , butyrate was shown to stimulate Na + absorption through both NHE2 and NHE3 activities (157). In C2bbe cells, however, only NHE3 and NHE8 but not NHE2 were stimulated by butyrate (207, 318). The observed increase in NHE3 activity in response to SCFA is at least in part due to transcriptional activation of NHE3 gene promoter, as both protein and mRNA were induced by SCFAs in vitro and in the colon of rats fed diet supplemented with 5% pectin (207).…”

“…This hypothesis was further supported by strong stimulation of the rat Nhe3 promoter activity by butyrate in transient transfection assays (148, 149). NHE8 is also regulated transcriptionally by butyrate via enhanced binding of Sp3 transcription factor to the proximal gene promoter (318). The concept of SCFA-activated colonic Na + /H + exchange has been explored to propose an alternative composition of the oral rehydration solution (ORS).…”

“…A proportion of the starch is broken down enzymatically in the small intestine to stimulate Na + absorption, while most of it would enter the colon where it could be fermented to SCFAs such as propionate, butyrate, and acetate by the resident bacteria. Butyrate increases the expression and/or activity of apical NHEs (4, 149, 157, 318) and aids in transepithelial Na + absorption via a neutral linked Na + absorptive process that exchanges SCFAs for OH − ions along with the apical Na + /H + exchange. In a small randomized clinical trial, this ORS formulation performed better than standard ORS by reducing both the duration and volume loss of severe acute diarrhea (247).…”

“…Transfection with the human NHE8 promoter reporter constructs in Caco2 cells showed that butyrate treatment stimulated NHE8 promoter activity at an amount comparable with its stimulation of NHE8 mRNA expression. Mechanistic study revealed an enhanced Sp3 protein binding on the human NHE8 basal promoter region upon butyrate stimulation, and that the effect of butyrate on NHE8 expression involves the acetylation of Sp3 transcriptional factor, a key protein regulating NHE8 basal transcription activation (318). …”

Pathophysiology of Intestinal Na+/H+ Exchange

“…Although some of the starch is broken down enzymatically in the jejunum to stimulate Na + absorption, most of it would enter the colon where it could be fermented to short-chain fatty acids such as propionate, butyrate, and acetate by the resident bacteria. Butyrate increases the expression and/or activity of apical NHEs85, 86, 87, 88 and aids in transepithelial Na + absorption via a neutral linked Na + absorptive process that exchanges short-chain fatty acids for OH - ions along with the apical Na + /H + exchange. In a small randomized clinical trial, this ORS formulation performed better than standard ORS by reducing both the duration and volume loss of severe acute diarrhea 84 .…”